The principal objectives of this research project are six-fold: 1) to determine host and viral factors which influence the genetically controlled resistance of inbred mouse strains to street rabies virus (SRV) 2) to determine if an in vivo laboratory model for persistent rabies virus infection can be established with subsequent goals of determining in which cell(s) the virus (genome) is sequestered and whether the virus can be activated to produce clinical disease 3) to understand the role of macrophages in rabies virus infections 4) to compare the protective capabilities of recombinant vaccines expressing different or multiple structural proteins of the rabies virus against genetic variants of rabies virus that have been isolated worldwide 5) to understand the complex interaction between microglial cells, lymphocytes and cytokines in the pathogenesis of rabies virus infections and 6) to determine the feasibility of using "naked DNA" vaccines to protect mice against a global spectrum of rabies virus variants. We have determined that tissue culture-adapted as well as wild "street" rabies viruses replicate in primary cultures of human, feline and murine microglia and astrocytes. Rabies viruses harvested from persistently- infected macrophage cell lines, after extended passages, lost virulence (failure to kill following ic inoculation). Virus isolated from these cells following incubation with IL-2 or PHA, reverted to virulence. Recombinant viruses expressing the glycoprotein (G) or both G and the nucleoprotein (N) (GN) of the rabies virus protected mice against a global spectrum of rabies virus variants. The strength (titer) and duration of the neutralizing antibody responses following vaccination with either recombinant were similar, as was the longevity of protection post-vaccination (100% protection at 18 months). An in vivo laboratory model of murine rabies virus persistence has been established. Viral genome has been detected in a variety of organs up to 469 days post-infection using a combination of techniques including organ culture, RT-PCR and Southern gel analysis. One microgram doses of our "naked" DNA vaccines encoding G have proven to be highly efficacious in inducing neutralizing antibody and cross-protecting mice against a global spectrum of rabies virus variants. Intradermal and gene-gun delivery of the DNA vaccines, as compared to IM-inoculation, were more effective in inducing protective immune responses. Adjuvants used with the DNA enhanced the primary neutralizing antibody responses, but had no enhancing effect on antibody responses when administered in combination with a "booster" DNA vaccination.